Apparatus and accompanying methods for achieving automatic color balancing in a film to video transfer system

Abstract

Apparatus and accompanying methods for use in a film to video transfer system for achieving automatic color balancing of color images for subsequent display on a color monitor. Specifically, this apparatus first transforms each pixel in an image to be transferred from logarithmic exposure ("log exposure") RGB color values into corresponding printing density values through local averaging, then utilizes a printing density based color correction method to generate a color correction offset value for each of the RGB primary colors, and finally converts the three resulting RGB color correction offset values from the printing density domain back to the log exposure domain wherein each offset value is subsequently used to correct the corresponding red, green and blue color values associated with each of the pixels that collectively forms a subsequent scan of the same image prior to the conversion of each of the color balanced RGB pixel values into analog video form.

I claim: 
     
       1. In a system for transferring an image from a first display format to a second display format, a method for balancing the colors present in the image prior to the image being transferred to said second display format, said method comprising the steps of: providing a first set of digitized color values in a first domain for each pixel in a scanned image, wherein each of said digitized color values in said first set is associated with a separate primary color in said image;   determining a set of local average values from said digitized color values that collectively form said scanned image, wherein each of said local average values is formed by averaging the digitized color values associated with a particular primary color for pixels that are situated within a pre-defined portion of said scanned image;   converting the local average values from the first domain to a second domain to provide converted local average values;   determining, in response to said converted local average values, a set of color correction offset values in said second domain, wherein each of said color correction offset values is associated with a particular one of said primary colors;   converting each of said color correction offset values from said second domain to said first domain so as to generate a set of color correction offset values, wherein each of said color correction offset values is associated with a corresponding one of said primary colors;   adding each one of said color correction offset values to a corresponding one of the color values in a second set of digitized color values in said first domain and associated with a corresponding primary color for each pixel in the scanned image in order to produce a set of color balanced color values in said first domain for each of said pixels in said image; and   providing, in response to each of said color balanced color values for each of said pixels in said scanned image, color balanced values in said second display format for each of the pixels in the scanned image.   
     
     
       2. The method in claim 1 wherein the color balanced values providing step comprises the step of correcting said set of color balanced color values for differences in tonescale between said first and second display formats to produce a set of gamma corrected color values. 
     
     
       3. The method in claim 2 wherein the color balanced values providing step further comprises the steps of: compensating said set of gamma corrected color values for a difference in chromatic response that occurs between said first and second display media in order to form a set of color compensated gamma corrected color values; and   converting said set of color compensated gamma corrected color values into said second display format.   
     
     
       4. The method in claim 3 wherein the local average values determining step comprises the steps of: accumulating the digitized color values for each group of a pre-defined number of horizontally contiguous pixels and for each of said primary colors so as to generate separate accumulated color values for each of said primary colors and for each of said groups;   determining, in response to each of said accumulated color values, an average color value associated therewith;   determining a corresponding one of said local average values as an average of the average color values for a pre-determined number of said groups associated with the same primary color and occurring in the pre-defined portion of said scanned image; and   repeating said accumulating, average color value determining and local average color value determining steps such that a local average value is obtained for each different pre-defined portion of said scanned image whereby said scanned image is partitioned into separate identically shaped paxels for each primary color and each paxel has a local average value associated therewith.   
     
     
       5. The method in claim 4 wherein the digitized color values providing step comprises the steps of: scanning said image to provide a stream of pixels in which each pixel has a single color analog value associated therewith;   digitizing each single color analog value in order to provide a stream of digitized single color pixel values;   converting each of said digitized single color pixel values into a logarithmic exposure domain as said first domain;   detecting an occurrence of a defective digitized single color pixel value and replacing said defective digitized single color pixel value in said stream of digitized single color pixel values with a most recent digitized single color pixel value for the same color as that of said defective single color digitized pixel in order to produce a stream of digitized corrected single color pixel values; and   re-constructing, in response to said stream of single color pixel values, said first set of logarithmic exposure primary color values for each pixel in the scanned image.   
     
     
       6. The method in claim 5 wherein the digitized color values that constitute said second set are the same values as those that constitute said first set or are associated with a scan of said image that occurred subsequent to a scan of said image that generated said first set and wherein said second domain is printing density. 
     
     
       7. The method in claim 4 wherein the color correction offset values determining step comprises the steps of: changing each of the converted local average values from a first primary color space to local average values in a pre-determined second color space;   determining, in response to each of said local average values in said second color space, transfer densities associated with each color in said second color space; and   determining, in response to said transfer densities, said color correction offset values.   
     
     
       8. The method in claim 7 wherein the digitized color values that constitute said second set are the same values as those that constitute said first set or are associated with a scan of said image that occurred subsequent to a scan of said image that generated said first set and wherein said second domain is printing density. 
     
     
       9. The method in claim 3 wherein the first display format is either photographic transparencies or photographic negatives and second display format is video. 
     
     
       10. The method in claim 9 wherein the second display converting step comprises the step of substantially simultaneously providing, in response to each set of said color corrected gamma corrected color values, either a composite NTSC analog video signal or separate analog RGB signals, wherein each of the analog signals corresponds to analog pixel information for either red, green or blue. 
     
     
       11. In a system for transferring an image from either a photographic transparency or photographic negative to an electronic video format, a method for balancing the colors present in the image prior to the image being transferred to said video format, said method comprising the steps of: providing a first set of digitized logarithmic exposure color values for each pixel in a scanned image, wherein each of said logarithmic exposure color values in said first set is associated with a separate primary color in said image;   determining a set of logarithmic exposure local average values from said logarithmic exposure color values that collectively form said scanned image, wherein each of said logarithmic exposure local average values is formed by averaging logarithmic exposure values associated with a particular primary color for pixels that are situated within a pre-defined portion of said scanned image;   converting the local average values from a logarithmic exposure domain to a printing density domain to provide converted local average values;   determining, in response to said converted local average values, a set of color correction offset values in said printing density domain, wherein each of said color correction offset values is associated with a particular one of said primary colors;   converting each of said color correction offset values from said printing density domain to said logarithmic exposure domain so as to generate a set of logarithmic exposure color correction offset values, wherein each of said logarithmic exposure color correction offset values is associated with a corresponding one of said primary colors;   adding each one of said logarithmic exposure color correction offset values to a corresponding one of the color values in a second set of digitized logarithmic exposure color values associated with a corresponding primary color for each pixel in the scanned image in order to produce a set of color balanced logarithmic color values for each of said pixels in said image;   correcting said set of color balanced logarithmic color values for differences in tonescale between either the transparency or the negative and the video format to produce a set of gamma corrected color values;   compensating said set of gamma corrected color values for a difference in chromatic response that occurs between said first and second display media in order to form a set of color compensated gamma corrected color values; and   converting said set of color compensated gamma corrected color values into the video format.   
     
     
       12. The method in claim 11 wherein the logarithmic exposure local average values determining step comprises the steps of: accumulating the logarithmic exposure color values for each group of a pre-defined number of horizontally contiguous pixels and for each of said primary colors so as to generate separate accumulated color values for each of said primary colors and for each of said groups;   determining, in response to each of said accumulated color values, an average color value associated therewith;   determining a corresponding one of said logarithmic exposure local average values as an average of the average color values for a pre-determined number of said groups associated with the same primary color and occurring in the pre-defined portion of said scanned image; and   repeating said accumulating, average color value determining and logarithmic exposure local average color value determining steps such that a logarithmic exposure local average value is obtained for each different pre-defined portion of said scanned image whereby said scanned image is partitioned into separate identically shaped paxels for each primary color and each paxel has a local average value associated therewith.   
     
     
       13. The method in claim 12 wherein the logarithmic exposure color values providing step comprises the steps of: scanning said image to provide a stream of pixels in which each pixel has a single color analog value associated therewith;   digitizing each single color analog value in order to provide a stream of digitized single color pixel values;   converting each of said digitized single color pixel values into the logarithmic exposure domain;   detecting an occurrence of a defective digitized single color pixel value and replacing said defective digitized single color pixel value in said stream of digitized single color pixel values with a most recent digitized single color pixel value for the same color as that of said defective single color digitized pixel in order to produce a stream of digitized corrected single color pixel values; and   re-constructing, in response to said stream of single color pixel values, said first set of logarithmic exposure primary color values for each pixel in the scanned image.   
     
     
       14. The method in claim 13 wherein the logarithmic exposure color values that constitute said second set are the same values as those that constitute said first set or are associated with a scan of said image that occurred subsequent to a scan of said image that generated said first set. 
     
     
       15. The method in claim 14 wherein the color compensated gamma corrected color values converting step comprises the step of substantially simultaneously providing, in response to each set of said color corrected gamma corrected color values, either a composite NTSC analog video signal or separate analog RGB signals, wherein each of the analog signals corresponds to analog pixel information for either red, green or blue. 
     
     
       16. Apparatus for transferring an image from a first display format to a second display format, wherein the apparatus balances the colors present in the image prior to transferring the image to said second display format, said apparatus comprising: means for providing a first set of digitized color values in a first domain for each pixel in a scanned image, wherein each of said digitized color values in said first set is associated with a separate primary color in said image;   means for determining a set of local average values from the digitized color values that collectively form said scanned image, wherein each of said local average values is formed by averaging the digitized values associated with a particular primary color for pixels that are situated within a pre-defined portion of said scanned image;   means for converting the local average values from the first domain to a second domain to provide converted local average values;   means for determining, in response to said converted local average values, a set of color correction offset values in said second domain, wherein each of said color correction offset values is associated with a particular one of said primary colors;   means for converting each of said color correction offset values from said second domain to said first domain so as to generate a set of color correction offset values, wherein each of said color correction offset values is associated with a corresponding one of said primary colors;   means for adding each one of said color correction offset values to a corresponding one of the color values in a second set of digitized color values in said first domain and associated with a corresponding primary color for each pixel in the scanned image in order to produce a set of color balanced color values for each of said pixels in said image; and   means for providing, in response to each of said color balanced color values for each of said pixels in said scanned image, color balanced values in said second display format for each of the pixels in the scanned image.   
     
     
       17. The apparatus in claim 16 wherein the means for providing color balanced values comprises means for correcting said set of color balanced color values for differences in tonescale between said first and second display formats to produce a set of gamma corrected color values. 
     
     
       18. The apparatus in claim 17 wherein the means for providing color balanced values further comprises: means for compensating said set of gamma corrected color values for a difference in chromatic response that occurs between said first and second display media in order to form a set of color compensated gamma corrected color values; and   means for converting said set of color compensated gamma corrected color values into said second display format.   
     
     
       19. The apparatus in claim 18 wherein the means for determining local average values comprises: means for accumulating the digitized color values for each group of a pre-defined number of horizontally contiguous pixels and for each of said primary colors so as to generate separate accumulated color values for each of said primary colors and for each of said groups;   means for determining, in response to each of said accumulated color values, an average color value associated therewith;   means for determining a corresponding one of said local average values as an average of the average color values for a pre-determined number of said groups associated with the same primary color and occurring in the pre-defined portion of said scanned image and for providing a corresponding local average value for each different pre-defined portion of said scanned image whereby said scanned image is partitioned into separate identically shaped paxels for each primary color and each paxel has a local average value associated therewith.   
     
     
       20. The apparatus in claim 19 wherein the means for providing the digitized color values comprises: means for scanning said image to provide a stream of pixels in which each pixel has a single color analog value associated therewith;   means for digitizing each single color analog value in order to provide a stream of digitized single color pixel values;   means for converting each of said digitized single color pixel values into a logarithmic exposure domain as said first domain;   means for detecting an occurrence of a defective digitized single color pixel value and replacing said defective digitized single color pixel value in said stream of digitized single color pixel values with a most recent digitized single color pixel value for the same color as that of said defective single color digitized pixel in order to produce a stream of digitized corrected single color pixel values; and   means for re-constructing, in response to said stream of single color pixel values, said first set of logarithmic exposure primary color values for each pixel in the scanned image.   
     
     
       21. The apparatus in claim 20 wherein the digitized color values that constitute said second set are the same values as those that constitute said first set or are associated with a scan of said image that occurred subsequent to a scan of said image that generated said first set and wherein said second domain is printing density. 
     
     
       22. The apparatus in claim 19 wherein the means for determining color correction offset values comprises: means for changing each of the converted local average values from a first primary color space to local average values in a pre-determined second color space;   means for determining, in response to each of said local average values in said second color space, transfer densities associated with each color in said second color space; and   means for determining, in response to said transfer densities, said color correction offset values.   
     
     
       23. The apparatus in claim 22 wherein the digitized color values that constitute said second set are the same values as those that constitute said first set or are associated with a scan of said image that occurred subsequent to a scan of said image that generated said first set and wherein said second domain is printing density. 
     
     
       24. The apparatus in claim 18 wherein the first display format is either photographic transparencies or photographic negatives and second display format is video. 
     
     
       25. The apparatus in claim 24 wherein the means for converting color compensated gamma corrected color values comprises means for substantially simultaneously providing, in response to each set of said color corrected gamma corrected color values, either a composite NTSC analog video signal or separate analog RGB signals, wherein each of the analog signals corresponds to analog pixel information for either red, green or blue. 
     
     
       26. Apparatus for transferring an image from either a photographic transparency or photographic negative to an electronic video format, wherein the apparatus balances the colors present in the image prior to transferring the image to said video format, said apparatus comprising: means for providing a first set of digitized logarithmic exposure color values for each pixel in a scanned image, wherein each of said logarithmic exposure color values in said first set is associated with a separate primary color in said image;   means for determining a set of logarithmic exposure local average values from said logarithmic exposure color values that collectively form said scanned image, wherein each of said logarithmic exposure local average values is formed by averaging logarithmic exposure values associated with a particular primary color for pixels that are situated within a pre-defined portion of said scanned image;   means for converting the local average values from a logarithmic exposure domain to a printing density domain to provide converted local average values;   means for determining, in response to said converted local average values, a set of color correction offset values in said printing density domain, wherein each of said color correction offset values is associated with a particular one of said primary colors;   means for converting each of said color correction offset values from said printing density domain to said logarithmic exposure domain so as to generate a set of logarithmic exposure color correction offset values, wherein each of said logarithmic exposure color correction offset values is associated with a corresponding one of said primary colors;   means for adding each one of said logarithmic exposure color correction offset values to a corresponding one of the color values in a second set of digitized logarithmic exposure color values associated with a corresponding primary color for each pixel in the scanned image in order to produce a set of color balanced logarithmic color values for each of said pixels in said image;   means for correcting said set of color balanced logarithmic color values for differences in tonescale between either the transparency or the negative and the video format to produce a set of gamma corrected color values;   means for compensating said set of gamma corrected color values for a difference in chromatic response that occurs between said first and second display media in order to form a set of color compensated gamma corrected color values; and   means for converting said set of color compensated gamma corrected color values into the video format.   
     
     
       27. The apparatus in claim 26 wherein the means for determining logarithmic exposure local average values comprises: means for accumulating the logarithmic exposure color values for each group of a pre-defined number of horizontally contiguous pixels and for each of said primary colors so as to generate separate accumulated color values for each of said primary colors and for each of said groups;   means for determining, in response to each of said accumulated color values, an average color value associated therewith;   means for determining a corresponding one of said logarithmic exposure local average values as an average of the average color values for a pre-determined number of said groups associated with the same primary color and occurring in the pre-defined portion of said scanned image and for providing a corresponding logarithmic exposure local average value for each different pre-defined portion of said scanned image whereby said scanned image is partitioned into separate identically shaped paxels for each primary color and each paxel has a local average value associated therewith.   
     
     
       28. The apparatus in claim 27 wherein the means for providing logarithmic exposure color values comprises: means for scanning said image to provide a stream of pixels in which each pixel has a single color analog value associated therewith;   means for digitizing each single color analog value in order to provide a stream of digitized single color pixel values;   means for converting each of said digitized single color pixel values into the logarithmic exposure domain;   means for detecting an occurrence of a defective digitized single color pixel value and replacing said defective digitized single color pixel value in said stream of digitized single color pixel values with a most recent digitized single color pixel value for the same color as that of said defective single color digitized pixel in order to produce a stream of digitized corrected single color pixel values; and   means for re-constructing, in response to said stream of single color pixel values, said first set of logarithmic exposure primary color values for each pixel in the scanned image.   
     
     
       29. The apparatus in claim 28 wherein the logarithmic exposure color values that constitute said second set are the same values as those that constitute said first set or are associated with a scan of said image that occurred subsequent to a scan of said image that generated said first set. 
     
     
       30. The apparatus in claim 29 wherein the means for converting color compensated gamma corrected color values comprises means for substantially simultaneously providing, in response to each set of said color corrected gamma corrected color values, either a composite NTSC analog video signal or separate analog RGB signals, wherein each of the analog signals corresponds to analog pixel information for either red, green or blue.